This invention relates to cementing pipe in a well drilled into the earth and more particularly is related to cementing pipe against evaporite sections penetrated by the well.
In the completion of a well drilled into the earth, pipe or casing is normally lowered into the well and a cement slurry is pumped down the well and up the annular spaced formed between the pipe and the wall of the well. The cement slurry is then maintained in the annular space to allow it to set and bond with the pipe and the wall of the well to thereby hold the pipe in place and to prevent fluids from flowing behind the pipe. Many different cements and cement slurries have been used for this purpose though portland cement and calcium aluminate cement are probably the most common cements. Various additives and formulations have been used with these cements in forming slurries having particularly desirable properties. For example, clays selected from the group of bentonite and attapulgite have been added to cement slurries as have sodium chloride, calcium chloride, dispersing agents, and gypsum.
In U.S. Pat. No. 3,197,317 to Freeman D. Patchen there is described a low density cement for use in wells. Patchen found that attapulgite may be added to portland cement slurries to effectively reduce the density of the slurry. U.S. Pat. No. 3,581,825 to Joseph U. Messenger was directed to a method of cementing wells wherein slurries of calcium aluminate cement and clay selected from the group of bentonite, attapulgite, and mixtures thereof, were used. These slurries were particularly applicable for use in cementing behind casing in permafrost zones. In U.S. Pat. No. 3,937,282 to Stanley H. Shryock et al. there is described another composition for cementing casing in wells drilled through permafrost zones. The Shyrock et al. slurry consists essentially of a hydraulic cement, gypsum, a monovalent chloride salt, and a setting time retarding agent and water. In U.S. Pat. No. 3,071,481 to Horace J. Beach et al. there is described a gel cement composition for use in cementing wells. This composition consists essentially of a hydraulic cement, a colloidal clay, sodium chloride or calcium chloride, and an organic dispersing agent. In U.S. Pat. No. 3,467,193 to Joseph U. Messenger there is described still another cement composition for use in cementing wells. This cement composition describes the use in a slurry of hydraulic cement of a turbulence inducer and silica or diatomaceous earth particles having sizes of from 0.1 to about 44 microns in diameter.